The invention relates to a sealing cover for preventing ingress of fluid between interengaging screw-threads of coaxially disposed inner and outer tubular members one of which is a pipe element which has a screw-threaded portion extending from one end and the other of which is a screw-threaded nipple which is in screw-threaded engagement with said screw-threaded end portion of the pipe element and has a first end which projects axially beyond said one end of the pipe element to protect the screw-thread on the end portion of the pipe element from damage by impact. In particular, although not exclusively, the invention is concerned with sealing covers for protecting the screw-threads formed on pipes such as the casing pipes of oil drilling rigs.
Such pipes with screw-threaded frusto-conical ends are at present delivered from manufacturers with the following end protection; one of the ends is fitted with a first internally screw-threaded, frusto-conical metal nipple and the other end is fitted with a metal coupling socket which is internally screw-threaded at both ends, one end receiving the screw-thread at the other end of the pipe and the other end of the coupling socket receiving a second, externally screw-threaded metal nipple so that the screw-threads at the opposite ends of the pipe and at the other end of the coupling socket are protected from damage by impact by the first nipple, by said one end of the coupling socket, and by the second nipple, respectively.
The disadvantage of this method of protection is that it is purely mechanical and is, in practice, ineffective against certain environmental conditions, since to make their insertion more convenient, the nipples and the coupling socket each have relieved ends which leave part of the screw-threads uncovered; in any case, of course, they do not comprise any device aimed at insulating the screw-threaded frusto-conical portions of the pipe and the coupling socket from environmental influences.
However, the casing pipes are usually used on offshore platforms or on continental desert sites and in a majority of cases are attacked by salty atmosphere, solar heat, winds and abrasive sands, and these climatic agents sometimes attack pipes together on the same site.
The metal nipples and coupling sockets at present used allow the penetration of sand, various dusts, air and rain which enter the pipes and coupling sockets and stagnate, attacking the screw-threads and neutralizing the grease applied when the casing pipe was finished and assembled with the coupling socket at the factory.
At many pipe storage locations, users have found that screw-threads were heavily damaged for the foregoing reasons, involving very high costs, because after a certain time in certain countries, the screw-threads rust and snap off, so that users are obliged to inspect their stores of pipes periodically, and this calls for considerable amounts of difficult handling (unscrewing the protective metal nipples and replacing them after greasing).
Clearly, in view of the working conditions unavoidably caused by the site where the pipes are kept, this is a serious problem and the known protection method has serious disadvantages.
Thus, as disclosed in U.S. Pat. Nos. 1,837,345; 2,134,730; 2,873,765 and 4,020,873, various solutions have been attempted to provide sealing covers which will protect the screw-threads of pipe elements. However, none of these solutions has provided adequate protection of the screw-threads against damage by impact and damage resulting from the ingress of fluid.